I had the same issue after rooting. Drivers worked fine to root, then after rooting, the fastboot drivers worked but not mtp.
Once I flashed a rom, everything was fine again.
So I would suggest doing a full wipe (minus internal storage) and then flashing a custom rom. Dirty Unicorns is a good one.
Either that or try using the factory images to return to stock.
The problem happens when you immediately flash the custom recovery after unlocking the bootloader. This should normally be fine but you can avoid this issue by booting back into the system after unlocking the bootloader and then flashing a custom recovery.
Like I said, once I flashed a rom, everything was all good again.